Large cargo vessels in particular transmit an identification signal, which forwards information about the ship, its position and speed, for example, to a coastal surveillance unit. Such information systems are designated, for example, as AIS (Automatic Identification System) or UAIS (Universal Automatic Identification System) and are usually based on radio transmission. By means of this transmitted signal, other vessels in the vicinity are also aware of the ships and their courses in the vicinity.
However, the problem with such systems is that they can be easily counterfeited. Especially in case of piracy, such radio signals can be completely switched off, or a ship signature can be transmitted to an entirely different ship, so that finding the captured ship can be very difficult.
In addition, marine traffic is monitored by radar systems. These radar systems are based on reflected radio waves, which are used to establish the size and distance of a ship. By tracking the ship over time, the course of the ship can also be determined by these means.
The problem with a radar monitoring system is that it relies on establishing a “line of sight”, as radio waves are generally not reflected back over the Earth's curvature. Thus, tracking a ship over the horizon is not possible. The AI and radar systems are used in parallel or supplementary to each other.